A better understanding of sleep and appetitive behavior is particularly relevant in view of the fact that a variety of common disorders of appetitive behaviors, such as eating disorders and substance abuse, often develop in adolescents, who are frequently sleep deprived. In rodents, prolonged sleep deprivation (SD) leads to weight loss, increased feeding, and increased energy expenditure. The mechanisms by which sleep and appetitive behaviors interact are currently unknown, but common pathways underlying these behaviors suggest possible ways they may interact. The nucleus accumbens (Acb) has well recognized participation in motivationally relevant behavior. Modulation of the Acb can result in alteration of appetitive instrumental behavior and feeding. We hypothesize that SD alters the motivational attributes of the Acb. To investigate this hypothesis, we will test sleep-deprived rats using tasks known to be dependent on the Acb. We will also compare changes in gene expression in the Acb and hypothalamus in sleep deprived versus normal control rats. Results from these studies will provide a comprehensive analysis of the effects of SD on the Acb and appetitive behavior.